Several approaches have been used, other than centrifugation, to separate erythrocytes from whole blood to perform rapid diagnostic assays. Specifically, one prior approach, as disclosed in U.S. Pat. Nos. 4,256,693 and 4,810,394 each to Masuda (the entire content of each prior patent being expressly incorporated hereinto by reference), uses successive layers of different materials to which whole blood is applied. Each layer in the multilayer blood separation media performs a separate function. One disadvantage associated with this prior approach is that a multi-layer separation media is expensive and difficult to manufacture.
Another approach to the problem of non-centrifugal separation of erythrocytes from whole blood, as disclosed in U.S. Pat. Nos. 4,477,575 and 4,816,224 each to Vogel et al. (the entire content of each prior patent being expressly incorporated hereinto by reference), uses a layer of glass microfiber having a density of 0.1-0.5 g/cm3 to separate erythrocytes from whole blood. One disadvantage to this prior approach is that papers or packings containing 100% glass microfibers are inherently weak and require extreme care in handling. Strength can be enhanced through the use of liquid binders such as acrylic or other latexes, acrylic or other synthetic resins or polyvinyl alcohol, but these binders can cause interference with the assay.
In another approach, as disclosed in U.S. Pat. No. 5,186,843 to Baumgardner et al. (the entire content of which is expressly incorporated hereinto by reference), a single-layer medium made of a composite of glass microfibers, cellulose fibers and synthetic staple fibers is used for separating erythrocytes from whole blood.
Although the blood separation media proposed in the past are suitable for their intended purpose, some improvements are still desired. For example, it would be desirable if a single layer media could be provided which performs substantially the same diagnostic functions and have substantially the same strength characteristics as compared to multilayer blood separation media. It would also especially be desirable if such a single-layer blood separation media could be formed completely of synthetic fibers. It is therefore towards fulfilling such needs that the present invention is directed.
Broadly, the present invention is embodied in blood separation media comprised of a non-woven web of fibrillated and non-fibrillated synthetic staple fibers. The fibrillated synthetic staple fibers will most preferably have a Canadian Standard Freeness (CSF) of less than about 300 mL, whereas the non-fibrillated synthetic staple fibers have a CSF of greater than about 700 mL.
In especially preferred forms, the present invention is embodied in blood separation media in which the fibrillated synthetic staple fibers are present in an amount between about 20 to 90 wt. %, and the non-fibrillated synthetic staple fibers are present in an amount between about 10 to about 80 wt. %. The fibrillated and non-fibrillated synthetic staple fibers may be formed of the same, or different, polymeric material, such as polyesters, polypropylenes, polyethylenes, poyacrylonitriles, and polyamides. Especially preferred blood separation media in accordance with the present invention will comprise a blend of fibrillated acrylic fibers, and a mixture of non-fibrillated nylon and polyester fibers, wherein the ratio of nylon and polyester fibers in the mixture thereof is between about 1:4 to about 1:2.
The blood separation media of this invention can be formed by conventional “wet-laid” processes. That is, an aqueous slurry of the fibrillated and non-fibrillated synthetic staple fibers may be formed and then subsequently dewatered to produce a non-woven web comprised of a blend of such fibrillated and non-fibrillated synthetic staple fibers.
In use, a quantity of whole blood may be brought into contact with the blood separation media for a time sufficient to separate the erythrocytes therein. More specifically, a quantity of whole blood is allowed to absorb into the blood separation media for a time sufficient to allow the plasma or serum to wick from the contact point a greater distance as compared to the erythrocytes. Such wicking, and hence erythrocyte separation, may occur radially (for example, parallel to the media surface) and/or vertically (for example, through the thickness of the media).
These aspects and advantages of the present invention will be further understood by reference to the following detailed description of a preferred exemplary embodiment thereof.